The reason has nothing to do with his own flip-flop-flip-flopping position on abortion rights. I believe he has, for decades, said whatever he felt he must to garner the support of the greatest possible number of voters. If he truly believed abandoning Mourdock two weeks before the election would bring a meaningful number of voters into his camp, he wouldn’t hesitate.
It is because he understands a reality about the forthcoming election, which I believe we should realize and take to heart ourselves: The election’s outcome will not be determined by undecideds (who no longer exist in any significant proportion, most having undoubtedly made up their minds weeks ago). It will be a function of the success of the two parties in compelling their supporters to go to the polls November 6th.
Romney and his handlers know this, and they know that virtually no one will switch their support from Romney to Obama because of Mourdock’s idiotic and indefensible position calling pregnancy "God's will" in cases of rape. But, he knows that many of his supporters (who swear their allegiance to the GOP and declare themselves likely voters when asked by robopolls, despite having never had any fondness whatsoever for Romney) would rather stay at work and bitch with their coworkers about how terrible things will be over the next four years, or spend the week in the woods hunting and drinking cheap beer, than actually get off their undoubtedly fat asses and go to the polls. So, Romney’s managers know that they must give their intended voters no reason to lose motivation, or to passive-aggressively avoid voting.
Standing by Mourdock will raise levels of alienation and discouragement among certain GOP voters, especially women, and this will undoubtedly hurt Romney to some degree Tuesday after next. But for him to forsake Mourdock would be seen by a broader base of GOP supporters as last-minute abandonment, and in doing so, he would be modeling turning his back on someone with whom he had made a previous commitment. This is what he does not want his own supporters to do, even passively by staying home or finding something better to do November 6th. It would cost him a much larger share of his current supporters.
We - from Obama and his campaign staff right down to the left-leaning citizen on the street - would do well to follow Romney’s example. We should realize that the battle for the presidency no longer involves recruiting people to our side; it is now a question of getting them to show up and fight.